1. Field of the Invention
The present invention relates to an image scanning apparatus adapted for use as an image input device for a printer, a copying apparatus or the like.
2. Related Background Art
The scanning apparatus of this kind is generally constructed that laser light emitted from a light source unit is condensed through a cylindrical lens into a linear form on a reflecting face of a polygon mirror of a deflecting device and is deflected into a scanning motion by the rotation of the polygon mirror, and is focused through an Fxcex8 lens onto the surface to be scanned of a photosensitive member in the form of a rotary drum, serving as the image bearing member.
In such mechanism, if the Fxcex8 lens is uneven in shape or is deviated in its mounting position, there will result a bending in the scanning line on the surface to be scanned or a biased magnification which is the difference between the lengths of the left and right half portions in the main scanning direction. Such bending of the scanning line or the biased magnification is permissible in case of forming a monochromatic image unless such bending or biased magnification becomes extremely large, but is not acceptable in case of forming a color image because plural scanning lines are to be superposed. More specifically, in order to form a high definition color image, it is required to reduce the bending of the scanning line and the biased magnification thereby reducing the displacement between the scanning lines of different colors.
Also in case a color image is formed by superposing images of each color on the surface to be scanned utilizing a single deflecting scanning apparatus and a single image bearing member, the bending of the scanning line and the biased magnification appear similarly in the each color, so that the out of color registration is retained within a certain extent. However, in case of forming a color image at a high speed by combining plural scanning apparatus and plural image bearing members, the bending of the scanning line and the biased magnification appear differently among different scanning apparatus so that the scanning lines of each color are mutually displaced even if they are registered in the sub scanning direction. It is therefore extremely difficult to form a high definition color image in such case.
On the other hand, light scanning apparatus for resolving such drawbacks are disclosed in the Japanese Patent Applications Laid-open Nos. 9-159944 and 11-190822. In the former, a transparent parallel-faced flat plate is added between the imaging lens and the image bearing member and is rotated about the longitudinal axis to correct the bending of the scanning line. In the latter, rod-shaped projections provided on both ends of the scanning lens and a central portion of the scanning lens are respectively pressed toward a V-shaped groove and a supporting pillar by an elastic member to suppress the positional displacement of the scanning resulting from the thermal expansion of the scanning lens.
However, in the scanning apparatus proposed in the Japanese Patent Application Laid-open No. 9-159944, the manufacturing cost is elevated because of the addition of the parallel-faced flat plate between the imaging lens and the image bearing member, and the biased magnification of the scanning line cannot be corrected.
Also in the scanning apparatus proposed in the Japanese Patent Application Laid-open No. 11-190822, as the elastic member is present within the effective image area of the scanning lens and presses the central portion thereof, the lens surface may be distorted to deteriorate the image. Also the entire length of the lens becomes larger because the rod-shaped projections are formed on both longitudinal ends of the lens. Consequently, in case the lens is molded with a plastic material, there may result a longer tact time of molding, a deteriorated precision of the lens surface or the diffracting surface or a reduced number of molded objects (articles) produced at a time from the mold, thus detrimentally affecting the manufacturing cost and the optical performance of the scanning lens. Furthermore, the biased magnification of the scanning line cannot be corrected as the adjustment of the scanning lens in the longitudinal direction is not considered.
In consideration of the foregoing, an object of the present invention is to provide an image scanning apparatus comprising:
deflection means for deflecting a light flux emitted from a light emitting source;
a lens for guiding the light flux deflected by the deflecting means to a surface to be scanned; and
a holding base for holding the lens, the holding member being provided with a recess portion;
wherein the lens has a curved surface portion on a lower face thereof and the holding base holds the curved surface portion by the recess portion.
Another object of the present invention is to provide an image scanning apparatus comprising:
deflection means for deflecting a light flux emitted from a light emitting source;
a lens for guiding the light flux deflected by the deflecting means to a surface to be scanned;
a holding member for holding the lens; and
a holding base for holding the holding member, the holding base being provided with a recess portion;
wherein the holding member has a curved surface portion and the holding base holds the curved surface portion of the holding member by the recess portion.
Still another object of the present invention is to provide an image scanning apparatus comprising:
deflection means for deflecting a light flux emitted from a light emitting source;
a lens for guiding the light flux deflected by the deflecting means to a surface to be scanned;
a first holding base for holding the lens; and
a second holding base for holding the lens by adhesion, the second holding base being vertically movable.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following detailed description which is to be taken in conjunction with the accompanying drawings.